Skyline Boulevard closing for dam project

Bicyclists and motorists have less than a week to enjoy the bridge that crosses Crystal Springs Dam before a three-year upgrade project breaks ground and forces them into a long detour.

A 1,300-foot segment of Skyline Boulevard between Crystal Springs Road and Bunker Hill Drive will be closed starting Oct. 21 as San Mateo County prepares to demolish the seismically vulnerable 1920s-era bridge that crosses the 121-year-old dam, officials said.

The bridge must be torn down so the San Francisco Public Utilities Commission can upgrade and improve the seismic safety of nearby water-distribution pipelines.

For Peninsula residents used to traveling the scenic roadway, the closure will mean a roughly four-mile detour over state Highway 92, up Polhemus Road and down Crystal Springs Road to emerge on the other side of the dam. Cyclists will have to use the Ralston Trail instead of Highway 92.

Some cyclists have concerns about the inconvenience, but the need to upgrade the aging infrastructure left officials with little choice, said Jim Porter, the county’s Public Works Department director.

“It’s one of those projects where the bridge was in need of replacement, SFPUC has to work on the dam and there are not a lot of other options,” Porter said.

Once the county finishes tearing the bridge down, a contractor for the commission is expected to begin about $20 million in work in spring 2011 to raise the height of the dam’s parapet wall by nine feet, widen the spillway and enlarge its stilling basin.

The upgrades will allow the reservoir to rise to levels not seen since 1983, when the state’s Division of Safety of Dams ordered the commission to lower water levels by eight feet due to concerns about the capacity of the spillway to safely handle a 100-year flood. The reduction shrunk the capacity of the reservoir by some 2.6 billion gallons.

Also, crews will perform roughly $100 million in seismic upgrades to pipelines, culverts and pumping facilities in the area. When the dam work is finished, the county plans to construct a $12 million bridge, paid for mostly by federal highway funds, and reopen Skyline Boulevard by the end of 2013.

The nearby Sawyer Camp Trail — which extends from San Bruno Avenue south to the dam and attracts 300,000 hikers, bikers and joggers per year — will remain open through most of the construction, though there will be occasional short-term closures, parks Director Dave Holland said.

As an added bonus, Holland said the county hopes to complete a long-planned extension of Sawyer Camp Trail down to Highway 92 while the dam upgrades are in progress.

“We should have that all connected by the time the dam’s completed,” Holland said.